Recently, much research and development is in progress of technology for improving light-emitting efficiency of an organic EL element (for instance, refer to Patent Literatures 1 and 2). A typical organic EL element includes: a TFT substrate; an anode; a cathode; an interlayer insulating layer; a charge injection layer; a light-emitting layer; and an electron transport layer. The anode serves as a bottom electrode in the organic EL element, and is formed on the TFT substrate with the interlayer insulating layer therebetween. Above the anode, the charge injection layer, the light-emitting layer, the electron transport layer, and the cathode, which serves as a top electrode in the organic EL element, are formed in the stated order. More specifically, the light-emitting layer is formed within each one of a plurality of apertures defined by a bank provided to the organic EL element. Further, in the organic EL element, either the top electrode or the bottom electrode is a reflective electrode, and the other one of the top electrode and the bottom electrode is a transparent electrode. Light emitted from the light-emitting layer is reflected by the reflective electrode and is guided out from the organic EL element from the side of the transparent electrode.
In the case of a top-emission type organic EL element, light is to be guided out from the side of the top electrode. As such, in a top-emission type organic EL element, the top electrode is the transparent electrode, and the bottom electrode is the reflective electrode. More specifically, a light-emitting layer included in a top-emission type organic EL element emits light in two directions, towards a bottom electrode and towards a top electrode. The light emitted by the light-emitting layer towards the bottom electrode is reflected by the bottom electrode and is guided out from the side of the top electrode, or that is, from the side of the transparent electrode. A reflective electrode in an organic EL element is commonly formed by using a metal film having high optical reflectivity (hereafter also referred to simply as “reflectivity”). By using a metal film having high reflectivity, the efficiency with which light is reflected by a reflective electrode can be improved, whereby the efficiency with which light is guided out from an organic EL element can be improved.
In specific, so as to provide a reflective electrode (i.e., an anode) with high reflectivity, a reflective electrode is commonly formed by using a film (an Ag film) composed of Ag or an alloy of Ag, or a film (an Al film) composed of Al or an alloy of Al. A reflective electrode is commonly formed by using Ag or Al since Ag and Al are metals having light-reflecting properties. Further, when performing a comparison between Ag films and Al films, Al films are superior in terms of cost than Ag films. Hence, the use of an Al film as a reflective electrode is more desirable compared to using an Ag film as a reflective electrode, especially when the size of a manufacturing target device, which includes organic EL elements, becomes greater.